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From: Pascal Roeleven <dev@pascalroeleven.nl>
To: Roman Beranek <roman.beranek@prusa3d.cz>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Emil Lenngren" <emil.lenngren@gmail.com>,
	"Lee Jones" <lee.jones@linaro.org>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Chen-Yu Tsai" <wens@csie.org>,
	linux-pwm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-sunxi@googlegroups.com
Subject: Re: [PATCH 0/6] pwm: sun4i: only wait 2 cycles prior to disabling
Date: Tue, 08 Jun 2021 14:28:53 +0200	[thread overview]
Message-ID: <8c3dd01c9a0b292771a3a557c247c087@pascalroeleven.nl> (raw)
In-Reply-To: <e63e2b31c63bb9e227ed9ec04a8af54e@pascalroeleven.nl>

On 2021-05-31 21:07, Pascal Roeleven wrote:
> On 2021-05-31 06:46, Roman Beranek wrote:
>> As Emil Lenngren has previously shown [1], actually only 1-2 cycles of
>> the prescaler-divided clock are necessary to pass before the PWM turns
>> off, not a full period.
>>
>> To avoid having the PWM re-enabled from another thread while asleep,
>> ctrl_lock spinlock was converted to a mutex so that it can be released
>> only after the clock gate has finally been turned on.
>>
>> [1] https://linux-sunxi.org/PWM_Controller_Register_Guide
>>
>> Roman Beranek (6):
>>   pwm: sun4i: enable clk prior to getting its rate
>>   pwm: sun4i: disable EN bit prior to the delay
>>   pwm: sun4i: replace spinlock with a mutex
>>   pwm: sun4i: simplify calculation of the delay time
>>   pwm: sun4i: shorten the delay to 2 cycles
>>   pwm: sun4i: don't delay if the PWM is already off
>>
>>  drivers/pwm/pwm-sun4i.c | 56 +++++++++++++++++++----------------------
>>  1 file changed, 26 insertions(+), 30 deletions(-)
> 
> Hi Roman,
> 
> Thanks for your attempt to fix this.
> 
> Unfortunately on my A10 device (Topwise A721), the controller still gets
> stuck in an unrecoverable state after disabling and re-enabling the PWM
> when it was already on (set in U-Boot), or when enabling it when it was
> off. In this state, any changes to the period register (using devmem)
> don't seem to have any effect. It seems to be stuck in the state it was
> before disabling. The only thing which still works is enabling and
> disabling.
> 
> I can't reproduce this behavior manually so I'm not sure what is causing
> this.
> 
> Regarding the amount of cycles of sleep; Using a prescaler of 72000 the
> PWM clock is 3 ms. Although timing tests using devmem seem unreliable
> (too much overhead?), in U-Boot I need to 'sleep' for at least 7 ms
> between the commands to make sure the output doesn't sometimes get stuck
> in the enabled state. So in my case it seems to be at least 3 cycles. I
> am not sure how reliable this method is. However even if I can get it
> stuck in the enabled state using a shorter time, it doesn't cause the
> behavior I mentioned before. I was always able to recover it manually.
> Increasing the number of cycles to sleep therefore also doesn't solve my
> problem. Until we can solve that I cannot confirm nor deny if 2 cycles
> is enough.
> 
> Regards,
> Pascal

Turns out, what I'm referring to here is actually a different issue not
related to this patch series. A different series might be sent later to
address that. 

So no objections from my side for this one.

Regards,
Pascal


      parent reply	other threads:[~2021-06-08 13:04 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-31  4:46 Roman Beranek
2021-05-31  4:46 ` [PATCH 1/6] pwm: sun4i: enable clk prior to getting its rate Roman Beranek
2021-06-07  8:00   ` Uwe Kleine-König
2021-05-31  4:46 ` [PATCH 2/6] pwm: sun4i: disable EN bit prior to the delay Roman Beranek
2021-06-07  8:07   ` Uwe Kleine-König
2021-05-31  4:46 ` [PATCH 3/6] pwm: sun4i: replace spinlock with a mutex Roman Beranek
2021-05-31  4:46 ` [PATCH 4/6] pwm: sun4i: simplify calculation of the delay time Roman Beranek
2021-05-31  4:46 ` [PATCH 5/6] pwm: sun4i: shorten the delay to 2 cycles Roman Beranek
2021-05-31  4:46 ` [PATCH 6/6] pwm: sun4i: don't delay if the PWM is already off Roman Beranek
2021-06-10 13:41   ` Pascal Roeleven
2021-05-31 19:07 ` [PATCH 0/6] pwm: sun4i: only wait 2 cycles prior to disabling Pascal Roeleven
2021-05-31 20:01   ` Emil Lenngren
2021-05-31 20:20     ` Pascal Roeleven
2021-06-08 12:28   ` Pascal Roeleven [this message]

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